JP3183935U - Piping joint structure and main steam piping - Google Patents

Abstract

The present invention provides a joint structure of a pipe and a main steam pipe, in which leakage before breakage of an internal fluid is established, and the characteristics against flow accelerated corrosion are sufficient.
A first pipe 11 and a second pipe 12 made of carbon steel containing Cr, and a weld metal portion 21 for welding ends of the first pipe and the second pipe to each other. The opposing end faces of the pipe and the second pipe are continuously connected to the inner peripheral surface of the first pipe and the second pipe, and are continuously welded to the outer peripheral side of the contact part. And an inclined portion 14 provided with the weld metal portion.
[Selection] Figure 1

Description

  The present invention relates to a joint structure for piping used in, for example, a nuclear power plant.

Conventionally, pipes including internal fluid such as main steam pipes of nuclear power plants are caused by fatigue or corrosion in the order shown in (1), (2), (3) as shown in FIG. 3, for example. It is assumed that the crack propagates. In FIG. 3, (A), (B), and (C) show the progress of cracks.
If the fracture toughness of the material constituting the pipe is low, such a crack may cause unstable fracture before the crack penetrates (for example, the state (2) in FIG. 3). In such a case, it will suddenly lead to destruction without any warning.

  In this way, when a crack propagates from the inner surface of the pipe, an unstable fracture occurs at the crack by detecting the internal fluid leaking through the crack at an early stage before the unstable fracture occurs. The concept of leak before break (hereinafter referred to as LBB) for safely stopping the nuclear power plant before is adopted in the piping design of the nuclear power plant.

In order to establish such an LBB, for example, various techniques for efficiently and quickly detecting leakage of an internal fluid that occurs before unstable fracture occurs are disclosed (for example, Patent Document 1). reference).
In addition, as a piping of the nuclear power plant mentioned above, a carbon steel pipe may be used from viewpoints of material strength, corrosion resistance, cost, etc.

JP 2002-106800 A

  By the way, regarding the establishment of LBB, the critical crack size (for example, (3) in FIG. 3) at which unstable fracture occurs is made larger than the crack size (for example, (2) in FIG. 3) at which penetration occurs. It is effective to easily detect the leakage of the internal fluid before the unstable fracture, and for this purpose, it is necessary to be made of a material having fracture toughness that does not cause unstable fracture at the time of crack penetration.

  On the other hand, as described above, carbon steel pipes may be used for piping of nuclear power plants (for example, main steam pipes), and when fluid flows inside the carbon steel pipes, flow accelerated corrosion (hereinafter referred to as Flow Accelerated Corrosion) Therefore, it is necessary to design the piping in consideration of this FAC. This FAC is a thinning phenomenon in which chemical corrosion of the metal constituting the piping is accelerated by the flow of the internal fluid.

  In addition, the pipe may have a joint structure in which the end faces of the pipe are welded to each other. In such a joint structure of the pipe, the above-described LBB must be established and the required characteristics for FAC must be satisfied. is there.

FIG. 4 shows a conventional joint structure 101 for piping. The pipe joint structure 101 includes a first pipe 111, a second pipe 112, and a weld metal part 121 that joins the first pipe 111 and the second pipe 112. As described above, when the weld metal portion 121 is formed on the inner peripheral surface side of the pipe and is in direct contact with the internal fluid, the characteristics with respect to the FAC may deteriorate.
An object of the present invention made there is to provide a joint structure of a pipe and a main steam pipe having an LBB and sufficient characteristics against FAC.

The present invention employs the following means in order to solve the above problems.
That is, the joint structure of the pipe of the present invention includes a first pipe and a second pipe made of carbon steel containing Cr, and a weld metal part that welds ends of the first pipe and the second pipe. The contact portions of the first piping and the second piping that are opposed to each other are continuously welded to the inner peripheral surfaces of the first piping and the second piping, and the outer peripheral side of the contact portions. And an inclined portion provided with the weld metal portion.

  According to the joint structure of the pipe of the present invention, the opposing end faces of the first pipe and the second pipe made of carbon steel containing Cr are continuously connected to the inner peripheral surfaces of the first pipe and the second pipe. Since it has the contact part welded, the inner peripheral surface side of piping will be comprised with the carbon steel containing Cr. That is, in the welded part of the first pipe and the second pipe, the inner peripheral surface side is formed by welding the first pipe and the second pipe containing Cr, and the weld metal part is not exposed to the inner peripheral surface side. While establishing LBB, the characteristic with respect to FAC is fully securable.

In the carbon steel, the Cr content is preferably more than 0.05 mass%.
Carbon steel with a Cr content of more than 0.05 mass% has LBB and good FAC characteristics. Therefore, by adopting a joint structure for piping using such carbon steel, The reliability of the joint structure can be improved.
Moreover, since it is set as the structure which a welding metal part does not expose to the inner peripheral surface side of piping as mentioned above, as a material which comprises a welding metal part, Cr content is less than the 1st piping and 2nd piping. A weld metal made of carbon steel can be used, and weldability can be secured.

In the carbon steel, the Cr content is preferably 0.40 mass% or less.
In this case, the manufacturing cost of the first pipe and the second pipe can be reduced.

The main steam pipe of the present invention is characterized by having the joint structure of the pipe described above.
According to the main steam pipe of the present invention, since it has the above-described pipe joint structure, LBB is established even in the pipe joint structure, and the characteristics against FAC are good. Can be improved.

  ADVANTAGE OF THE INVENTION According to this invention, while LBB is materialized, the joint structure of piping with sufficient characteristic with respect to FAC, and main steam piping can be provided.

It is a schematic explanatory drawing of the joint structure of piping concerning the embodiment of the present invention. It is a figure which shows the relationship between J integral value of the fracture toughness of piping which concerns on embodiment of this invention, and tearing modulus. It is the schematic for demonstrating the progress of the crack in piping. It is a schematic explanatory drawing of the joint structure of the conventional piping.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
Embodiment of this invention is the joint structure 1 of the piping which the main steam piping of a nuclear power plant (PWR, pressurized water nuclear reactor) has, for example. FIG. 1 shows a joint structure 1 for piping according to an embodiment of the present invention.

As shown in FIG. 1, the pipe joint structure 1 includes a first pipe 11 and a second pipe 12, and a weld metal part 21 that welds the ends of the first pipe 11 and the second pipe 12. ing.
The first piping 11 and the second piping 12 are cylindrical piping, and high-temperature and high-pressure steam flows as an internal fluid inside the piping. In FIG. 1, a part of the longitudinal section of the first pipe 11 and the second pipe 12 is shown. In FIG. 1, the lower side is the inner side of the first pipe 11 and the second pipe 12, and the upper side is the outer side of the first pipe 11 and the second pipe 12.

  The first pipe 11 and the second pipe 12 are made of carbon steel containing Cr. In the carbon steel, the Cr content is preferably more than 0.05 mass% and not more than 0.40 mass%, more preferably 0.10 mass% to 0.40 mass%. The thickness of the first pipe 11 and the second pipe 12 (thickness indicated by H1 in FIG. 1) is, for example, 40 mm.

  And each end surface which opposes among the above-mentioned 1st piping 11 and the 2nd piping 12 is the contact part 13 where the 1st piping 11 and 2nd piping 12 were welded, and the inclination part in which the weld metal part 21 is provided 14.

  The contact portion 13 is formed by continuously welding to the inner peripheral surfaces of the first pipe 11 and the second pipe 12. That is, in the welded portion of the first pipe 11 and the second pipe 12, the first pipe 11 and the second pipe 12 containing Cr on the inner peripheral surface side are welded. However, the welding material of carbon steel used when joining the contact portion 13 takes into account that Cr contained in the first pipe 11 and the second pipe 12 is diluted by welding, and the first pipe 11 and the second pipe. A welding material with the same Cr content as 12 must be selected.

  The contact portion 13 is formed by the heat that flows when the weld metal portion 21 is welded, and the first pipe 11 and the second pipe 12 by the welding material having the same Cr content as the first pipe 11 and the second pipe 12 described above. The ends of the two pipes 12 are formed by welding. For example, arc welding may be used as the welding method.

  The thickness of the contact portion 13 (thickness indicated by H2 in FIG. 1) is set to a thickness that sufficiently melts the first pipe 11 and the second pipe 12 in the one-side welding and forms a back wave during the above-described welding. Yes. Specifically, for example, when H1 is 40 mm, H2 is 1.5 mm or more and 3 mm or less.

  The inclined portion 14 is a groove formed to provide the weld metal portion 21 when the first pipe 11 and the second pipe 12 are welded, and is continuously formed on the outer peripheral side of the contact portion 13. In the present embodiment, the inclined portion 14 is formed in an oblique direction with respect to the extending direction of the first pipe 11 and the second pipe 12, and the outer periphery from the inner peripheral surface side of the first pipe 11 and the second pipe 12. The inclination is gradually increased toward the surface side. In this embodiment, the cross-sectional shape of the groove | channel which the 1st piping 11 and the 2nd piping 12 faced is made into the U-shaped groove | channel. The inclined portions 14 of the first pipe 11 and the second pipe 12 are separated from each other so that a weld metal is interposed therebetween.

The weld metal part 21 is a member for welding the first pipe 11 and the second pipe 12, and is provided in the inclined part 14 formed by abutting the ends of the first pipe 11 and the second pipe 12. Yes. It is preferable that this weld metal part 21 is comprised with the carbon steel which contains Cr 0.01 mass% or more and 0.05 mass% or less.
The weld metal part 21 is formed by welding the bead which comprises the weld metal part 21, for example by arc welding.

Below, the experimental result performed in order to confirm the establishment of LBB with respect to the carbon steel containing Cr is shown.
The establishment of the LBB is performed by determining whether the relationship between the J-integral value of the fracture toughness of the material to be evaluated and the tearing modulus is equal to or higher than the LBB required line. Here, the J-integral value and tearing modulus of fracture toughness can be obtained, for example, by performing a fracture toughness test on the material to be used. FIG. 2 shows the case where SF (stress factor, measured value of tensile strength / spec value of tensile strength) = 1.2 as the required line of LBB, but the required line of LBB is the value of this SF. What is necessary is just to set suitably according to.

  FIG. 2 shows the relationship between the J integral value of fracture toughness and tearing modulus obtained for a weld metal of carbon steel containing about 0.01 mass% of Cr. 2 is a curve obtained experimentally using a test piece having a thickness of 1.5 inches, and curves b and c are test pieces having a thickness of 1 inch. It is the curve calculated | required experimentally using.

As shown in FIG. 2, the weld metal of carbon steel containing 0.01 mass% of Cr exceeded the required line of LBB, and it was confirmed that LBB was established.
In addition, the specific composition of the weld metal of carbon steel containing about 0.01 mass% of Cr used in the experiment is C: 0.07 mass%, Mn: 1.46 mass%, P: 0.006 mass%, S : 0.009 mass%, Si: 0.81 mass%, Cr: 0.01 mass%, Cu: 0.19 mass%, Mo: less than 0.01 mass%, Ni: 0.02 mass%, V: less than 0.001 mass%, The balance consists of Fe and other inevitable impurities.

  Moreover, the characteristic with respect to the FAC with respect to the carbon steel containing Cr has description in the report (NSAC-202L-R3) by EPRI (Electric Power Research Institute). According to this report, it can be seen that, in carbon steel containing 0.10% Cr, the characteristics with respect to FAC are greatly improved as compared with carbon steel not containing Cr. That is, carbon steel containing Cr has good characteristics with respect to FAC. In addition, the characteristic with respect to FAC will improve if Cr content increases in carbon steel.

  According to the pipe joint structure 1 according to the present embodiment configured as described above, the opposing end faces of the first pipe 11 and the second pipe 12 made of carbon steel containing Cr are the first pipe. 11 and the inner peripheral surface of the second pipe 12 are continuously welded to each other, so that the inner peripheral surface side of the pipe is constituted by carbon steel containing Cr. As well as being established, the characteristics for FAC can be sufficiently secured.

In the carbon steel, since the Cr content is preferably more than 0.05 mass%, in this case, LBB is surely established and the characteristics against FAC are also improved. The Cr content is more preferably 0.10 mass% or more. In this case, the LBB is more reliably established and the characteristics with respect to the FAC are further improved.
Further, in the carbon steel, the Cr content is preferably 0.40 mass% or less, and in this case, the manufacturing cost of the first pipe 11 and the second pipe 12 can be reduced.

  The weld metal part 21 is preferably made of carbon steel containing 0.01 mass% or more and 0.05 mass% or less of Cr, so that weldability can be ensured. That is, when the Cr content of the weld metal part 21 exceeds 0.05 mass%, the weldability decreases.

  When the Cr content in carbon steel increases, LBB is easily established and the characteristics with respect to FAC are also improved. Therefore, in the conventional pipe joint structure 101 as shown in FIG. If it can be composed of carbon steel with a mass exceeding 0.05 mass%, it is considered that LBB can be established and the characteristics against FAC are improved, but from a carbon steel with a Cr content exceeding 0.05 mass%. Since the weld metal which becomes is deteriorated in weldability, it is difficult to use the weld metal in the weld metal portion 21. Therefore, in the present embodiment, the first pipe 11 and the second pipe 12 are preferably made of carbon steel having a Cr content exceeding 0.05 mass%, and the contact portions 13 of the first pipe 11 and the second pipe 12 are configured. Since the first pipe 11 and the second pipe 12 are on the inner peripheral surface side in the welded portion, the LBB can be established reliably and the characteristics with respect to the FAC can be reliably improved.

  The embodiment of the present invention has been described above, but the present invention is not limited to this, and can be appropriately changed without departing from the technical idea of the present invention.

  In the above embodiment, the case where the inclined portions 14 of the first pipe 11 and the second pipe 12 are abutted to form a U-shaped groove has been described. It may be V-shaped.

DESCRIPTION OF SYMBOLS 1,101 Piping joint structure 11,111 1st piping 12,112 2nd piping 13 Contact part 14 Inclined part 21,121 Weld metal part

Claims (4)

A first pipe and a second pipe made of carbon steel containing Cr;
A welded metal part for welding the ends of the first pipe and the second pipe,
Each of the opposing end faces of the first pipe and the second pipe is
A contact portion that is welded continuously to the inner peripheral surface of the first pipe and the second pipe;
A joint structure for piping, comprising: an inclined portion continuously formed on the outer peripheral side of the contact portion and provided with the weld metal portion.   The joint structure for piping according to claim 1, wherein the carbon steel has a Cr content of more than 0.05 mass%.   The pipe joint structure according to claim 1 or 2, wherein the carbon steel has a Cr content of 0.40 mass% or less.   The main steam piping which has the joint structure of piping as described in any one of Claims 1-3.

Images